There is a wideband-code division multiple access (W-CDMA) scheme which is one of wireless communication schemes. The W-CDMA scheme is one of wireless communication interfaces defined as the International Mobile Telecommunications-2000 (IMT-2000) and is regarded as one of the representative wireless communication schemes.
The W-CDMA scheme enables multimedia accesses of voice, videos, data, or the like, at a transmission speed of up to 384 kbps.
In addition, wireless communication schemes known as the high-speed downlink packet access (HSDPA) and the high-speed uplink packet access (HSUPA) on the basis of the technique of the W-CDMA scheme have been researched and developed recently.
The HSDPA is a technique for achieving a high-speed downlink packet transmission in the downlink direction which is the direction from a base station (BS) to a terminal (user equipment: UE). The HSUPA is a technique for achieving a high-speed uplink packet transmission at the uplink direction which is the opposite to the direction of the HSDPA. The HSDPA is standardized as the 3rd Generation Partnership Project Release 5 (3GPP release 5) and the HSUPA is standardized as the 3GPP release 6.
FIG. 5 is a conceptual drawing illustrating communications according to the W-CDMA. As depicted in FIG. 5, a wireless communication is carried out between a base station (BS) 100 and one or more terminals (UEs) 200 according to the W-CDMA scheme.
For the uplink, the dedicated physical data Channel (DPDCH) that is a channel for transmitting user information and the dedicated physical control channel (DPCCH) that is a channel for transmitting control information are each mapped to the in-phase component (I axis) and the quadrature component (Q axis) of the quadrature phase shift keying (QPSK) modulation and sent to the BS 100 (see solid line arrow A1).
For the downlink, the DPDCH and the DPCCH are time division multiplexed and sent to the UEs 200 (see dashed line arrow A2). Note that these links are discrete channels that are allocated to each UE 200 in order to carry out transmission exclusive relative to other UEs 200.
Next, the concept of the communication of the HSDPA is illustrated in FIG. 6. As depicted in FIG. 6, communications according to the HSDPA are carried out for downlink transmission from the BS 100 to the UEs 200.
More specifically, each UE 200 receives a pilot signal (a signal commonly recognized by the BS 100 and the UE 200) sent from the BS 100 on a pilot channel (CPICH: common pilot channel) (see reference symbol A5), measures the transmission environment, i.e., the reception quality (signal interference ratio: SIR) of the downlink on the basis of the pilot signal for that UE 200, calculates an channel quality indicator (CQI) report value that is the reception quality value on the downlink on the basis of the measurement result, and reports the CQI report value to the BS 100 on a high-speed dedicated physical control channel (HS-DPCCH) (see solid line arrow A3).
The BS 100 carries out scheduling to select preferentially a predetermined number of UEs 200 that have better transmission environments on the basis of the reception quality value (CQI report values) reported by the UEs 200. Suppose a certain UE 200 is selected as a result of the scheduling, the BS 100 notifies that UE 200 of scheduling information (including the type of modulation, the transmission volume, or the like) on a high-speed shared control channel (HS-SCCH) (see dashed line arrow A4). The UE 200 sets the functions of the local terminal 200 on the basis of the received scheduling information.
The BS 100 then sends user information to the UE 200 on a wireless channel called a high-speed physical downlink shared channel (HS-PDSCH) (see dashed line arrow A4). The HS-PDSCH for transmitting the user information is a common channel that are used by each of the UEs 200 wherein one time-divided time slot is shared by one UE 200 or multiple UEs 200, enabling a high-speed downlink access of up to 14.4 Mbps.
The concept of the communication of the HSUPA is now illustrated in FIG. 7. As depicted in FIG. 7, communications according to the HSUPA are carried out for uplink transmission from the UEs 200 to the BS 100.
More specifically, the UEs 200 send scheduling information (SI) as uplink data transmission requests to the BS 100 (see solid line arrow A6).
The BS 100 sums the multiple SIs sent from the UEs 200, carries out scheduling to determining the transmission timings for the UEs 200 to carry out an uplink transmission on the basis of communication qualities of the UEs 200, priorities of uplink data, or the like, and sends a Grant to an UE 200 as an uplink transmission permission (see dashed line arrow A7). Note that there are two types of Grants, namely, absolute grants and relative grants, wherein absolute grants are used for notifying uplink transmission rates or the like at a predetermined intervals, and relative grants are used for notifying update of the information that has been notified the absolute grant.
The UEs 200 send user information to the BS 100 via respective channels called enhanced dedicated channels (E-DCHs) in the order of permissions given to the terminals 200 to carry out an uplink transmission by receiving a Grant from the BS 100 (see solid line arrow A8), thereby enabling a high-speed uplink access. Note that it is considered that the transmission speed of the E-DCH will be 2-5 Mbps.
The HSDPA employs the adaptive code modulation scheme, and for example, is characterized in that the QPSK modulation scheme and the 16QAM modulation scheme are switched adaptively according to the wireless environment between the BS 100 and the UEs 200. In addition, in order to achieve an adaptive modulation scheme as described above, CQI report values used by the UEs 200 to report the reception environments to the BS 100 are defined wherein different formats of different transmission speeds are defined according to CQI=1 to 30, for example, in a CQI table.
Each UE 200 then measures the reception environment, and basically reports the maximum CQI report value to the BS 100 not exceeding the block error rate (BLER) (=0.1) of the HS-PDSCH supposing that the HS-PDSCH is received within three slots after one slot before the CQI report value is sent in the environment.
Here, one example of the CQI table is illustrated in FIG. 8. As depicted in FIG. 8, each of the CQI report values from the UEs 200 is related to a transport block size of downlink data, and the BS 100 determines a transport block size of the downlink data and a downlink transport format on the basis of a CQI report value from an UE 200.
On the other hand, on the HSUPA, the BS 100 monitors the total uplink interference (reception power) of its own base station, and compares the reception power with a threshold value. Thereby, the BS 100 designates a transmission rate in an absolute value to an UE 200 that has an uplink transmission request using an E-AGCH (command to designate an absolute value of the maximum rate), or commands the UE 200 to increase, maintain or decrease the transmission rate using or an E-RGCH (command to designate relative value of the maximum rate). When the UE 200 has uplink transmission data, the UE 200 sends a scheduling request (SI) to the BS 100.
Note that there are techniques disclosed in the following Patent Documents 1-3 as techniques related to methods for controlling scheduling in the W-CDMA including the HSUPA.
The following Patent Document 1 discloses that a wireless base station assigns an upper limit of the uplink packet rate that is permitted to a mobile station according to the downlink CQI report value received from the mobile station. The following Patent Document 2 discloses that a base station switches a mobile terminal from the scheduling mode that is currently used for uplink transmission to another scheduling mode on the basis of the estimated buffer occupation. In addition, the following Patent Document 3 discloses that a base station enhances the utilization efficiency of the uplink by broadcasting a certain second indication indicating statuses of all user terminals using a common channel.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-140635    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-60789    Patent Document 3: Japanese Laid-Open Patent Publication No. 2006-87100
When downlink data received on the HS-PDSCH undergoes required L2 data processing and at least part of the downlink data is sent to the BS 100 in real-time on the E-DCH, for example, the communication rate in the uplink direction may differ from the communication rate in the downlink direction due to the difference in the communication environment in the downlink direction (i.e., the data transmission direction from the BS 100 to the UEs 200) and the communication environment in the downlink direction (i.e., the data transmission direction from the UEs 200 to the BS 100), scheduling processing at the BS 100, or the like. For this reason, the UEs 200 are adapted to absorb the above-described difference in the communication rates by storing uplink data to the buffer.
However, when the communication rate in the uplink direction becomes lower than the communication rate in the downlink direction due to HSUPA scheduling processing by the BS 100, for example, data storage processing (buffer processing) to the buffer may be delayed and the buffer may overflow. As a result, data communication processing may be hindered from being executed correctly.
None of Patent Documents 1-3 described above discloses or suggests such issues and solutions for the issues.